Floating wind turbine blade pitch adjustment for wave activity

ABSTRACT

Provided is a method, computing system, and computer program product for reducing floating wind turbine loads induced by ocean waves by adjusting a blade pitch angle of at least one rotor blade of a floating wind turbine to minimize a moment imbalance at a platform top of the floating wind turbine caused by ocean wave activity.

FIELD OF TECHNOLOGY

The following relates to embodiments of blade pitch adjustment forfloating wind turbines, and more specifically to embodiments of a methodfor reducing loads induced by ocean waves on floating wind turbinetowers.

BACKGROUND

Floating wind turbines experience environmental disturbances that areinduced from different sources, like turbulence, aeroelastic effects,and ocean waves. The loads caused by ocean waves contribute asignificant portion of the overall floating wind turbine cost.Conventional methods address fatigue loads at the wind turbine/floatingplatform interface by over-designing the connection components or bycurtailing extraction of energy available in the environment, but thesemethods add complexity and cost to floating wind turbine towerconstruction and operation.

SUMMARY

An aspect relates to a method for reducing floating wind turbine loadsinduced by ocean waves. A blade pitch angle of at least one rotor bladeof a floating wind turbine is adjusted to minimize a moment imbalance ata platform top of a floating wind turbine caused by ocean wave activity.

In an exemplary embodiment, the method includes calculating an errorsignal based on the moment imbalance measured between a tower bottommoment and a thrust moment. The tower bottom moment is a moment at aplatform top of the floating wind turbine as a result of environmentalloads, and the thrust moment is a moment defined by a thrust force ofrotor blades of the floating wind turbine measured at a location on theshaft of the floating turbine proximate the platform top.

In an exemplary embodiment, the method includes filtering the errorsignal using a bandpass filter in a frequency range attributable toocean wave activity to obtain a filtered error signal. The filteringisolates wave excitation frequencies from the error signal that are inthe frequency range defined by an ocean wave spectrum. The blade pitchangle is adjusted according to a pitch offset signal converted from thefiltered error signal. The pitch offset signal is converted from thefiltered error signal by calculating a difference between an actualpitch angle value of at least one rotor blade and a desired blade pitchangle of at least one rotor blade, wherein the difference defines thepitch offset signal.

Another aspect relates to a method for reducing loads induced by oceanwaves on a floating wind turbine. A processor of a computing systemcalculates an error signal defined by a moment imbalance between a towerbottom moment and a thrust moment of the floating wind turbine. Theerror signal is filtered in a frequency range attributable to ocean waveactivity to eliminate frequencies contributing to the error signal thatare not attributable to ocean wave activity, resulting in a filterederror signal. The filtered error signal is converted to a pitch offsetsignal. A blade pitch angle of at least one rotor blade of the floatingwind turbine is adjusted according to the pitch offset signal.

In an exemplary embodiment, the error signal comprises frequenciesattributable to one or more of: turbulence due to wind above sea level,ocean wave activity, ocean current variability, vortex inducedvibrations, structural resonances, electrical grid phenomena, and normalturbine operations. Moreover, the error signal is filtered using abandpass filter tuned to filter out frequencies above or below thefrequency range attributable to ocean wave activity; the frequency rangeattributable to ocean wave activity is defined by an ocean wavefrequency spectrum in a range of approximately 0.03 Hz to 0.25 Hz.

In an exemplary embodiment, the filtered error signal is converted tothe pitch offset signal includes calculating a difference between anactual pitch angle value of at least one rotor blade and a desired bladepitch angle of at least one rotor blade, wherein the difference definesthe pitch offset signal. By way of example, the pitch offset signal iscalculated from the filtered error signal according to a function withthe following properties: a term proportional to a current value of thefiltered error signal, a term proportional to a time integral of thefiltered error signal, and a term proportional to a time derivative ofthe filtered error signal

Another aspect relates to a computer system, comprising: a processor, amemory device coupled to the processor, a pitch controller coupled tothe processor, and a computer readable storage device coupled to theprocessor, wherein the storage device contains program code executableby the processor via the memory device to implement a method forreducing loads induced by ocean waves on a floating wind turbine tower.

Another aspect relates to a computer program product, comprising acomputer readable hardware storage device storing a computer readableprogram code, the computer readable program code comprising an algorithmthat when executed by a computer processor of a computing systemimplements a method for reducing loads induced by ocean waves on afloating wind turbine tower.

The foregoing and other features of construction and operation will bemore readily understood and fully appreciated from the followingdetailed disclosure, taken in conjunction with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the embodiments will be described in detail, with reference tothe following figures, wherein like designations denote like members,wherein:

FIG. 1 depicts a schematic view of a floating wind turbine, inaccordance with embodiments of the present invention;

FIG. 2 depicts a block diagram of a blade pitch control system, inaccordance with embodiments of the present invention;

FIG. 3 depicts a block diagram of an alternative blade pitch controlsystem, in accordance with embodiments of the present invention;

FIG. 4 depicts a schematic view of the floating wind turbine of FIG. 1,showing a thrust moment and a tower bottom moment, in accordance withembodiments of the present invention;

FIG. 5 graphically depicts the error signal being filtered so thatfrequencies only within the range of the ocean wave spectrum pass whilethe frequencies outside the ocean wave spectrum are stopped;

FIG. 6 depicts a flow chart of a method for reducing loads induced byocean waves on a floating wind turbine, in accordance with embodimentsof the present invention;

FIG. 7 depicts a flowchart of a converting step of the method forreducing loads induced by ocean waves on a floating wind turbine, inaccordance with embodiments of the present invention;

FIG. 8 depicts a schematic block diagram of the blade pitch angleadjustment of the method for reducing loads induced by ocean waves on afloating wind turbine, in accordance with embodiments of the presentinvention; and

FIG. 9 depicts a block diagram of a computer system for the blade pitchcontrol system of FIGS. 1-5, capable of implementing methods forreducing loads induced by ocean waves on a floating wind turbine ofFIGS. 6-8, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

A detailed description of the hereinafter described embodiments of thedisclosed apparatus and method are presented herein by way ofexemplification and not limitation with reference to the Figures.Although certain embodiments are shown and described in detail, itshould be understood that various changes and modifications may be madewithout departing from the scope of the appended claims. The scope ofthe present disclosure will in no way be limited to the number ofconstituting components, the materials thereof, the shapes thereof, therelative arrangement thereof, etc., and are disclosed simply as anexample of embodiments of the present disclosure.

As a preface to the detailed description, it should be noted that, asused in this specification and the appended claims, the singular forms“a”, “an” and “the” include plural referents, unless the context clearlydictates otherwise.

In brief overview, floating wind turbine towers experience loads frommany environmental sources, such as wind and ocean waves. Ocean waveactivity, particularly those that the submerged portion of the platformtop of the floating wind turbine is subjected to, result in loads thatmust be counteracted for proper operation and structural integrity ofthe floating wind turbine. Rather than counteracting the ocean waveloads by designing a more robust platform top, which adds to the cost,weight, and complexity of the structure, embodiments of the presentinvention reduce the floating platform loads induced by ocean waves byregulating and/or adjusting a blade pitch angle of one or more rotorblades of the floating wind turbine. Adjusting the blade pitch angle ofthe rotor blades can mitigate a floating wind turbine tower-bottombending moment and floating platform interface fatigue loads. Forinstance, adjusting the blade pitch angle of at least one rotor bladecan minimize a moment imbalance at a platform top of the floating windturbine tower caused by ocean wave activity.

A moment imbalance on the floating wind turbine tower bottom is adifference between a measured tower bottom moment and a moment createdby a rotor thrust force measured at the shaft, or alternatively, at ablade root (i.e. thrust moment). The tower bottom moment is a moment atthe platform top of the floating wind turbine tower as a result ofenvironmental loads, and the thrust moment is a moment defined by athrust force of rotor blades of the floating wind turbine tower measuredat a location of a shaft of the floating turbine tower proximate theplatform top. The difference between the tower bottom moment and thethrust moment is calculated and output as an error signal by a controlmechanism (i.e. computing system). Because the error signal containsdisturbances related to both ocean activity and other disturbances not aresult from ocean activity, the error signal is filtered by the controlmechanism to isolate the frequencies associated with ocean activity,known as “wave excitation frequencies.” The error signal is filteredusing a filter, such as a bandpass filter, in a frequency range definedby an ocean wave spectrum. The ocean wave spectrum is the frequencyrange where ocean waves are observed to exist. In this way, the filterederror signal focuses only on the effects of ocean wave activity. Thefiltered error signal of the imbalance is then converted to a pitchoffset signal that is used by the control mechanism to adjust a bladepitch angle of the rotor blades. Accordingly, the moment imbalance iscounteracted by pitch control of the blades so that the tower bottommoment and the thrust moment cancel each other out, thereby reducingand/or eliminating loads against the platform top of the floating windturbine tower induced by ocean waves.

Referring now to the drawings, FIG. 1 depicts a schematic view of afloating wind turbine 1, in accordance with embodiments of the presentinvention. The floating wind turbine 1 includes one or more rotor blades5 that connect to a hub 6 of the floating wind turbine 1. The hub 6 isconnected to a nacelle 3 that is atop a wind turbine tower 4. The windturbine tower 4 may be constructed in multiple sections, such as towersection 9 and tower section 10, or may be a single tower section. Thetower 4 extends from the nacelle 3 to a transition piece 7; the locationwhere a tower bottom 8 meets a platform top 11 is called a transitionpiece or transition section 7. A platform hull 12 is located proximateor at the surface of the water and extends below the surface of thewater. The platform hull 12 is designed to float in the water whilesupporting the floating wind turbine 1 at offshore locations. Althoughshown schematically in FIG. 1 as comprising a single base structure, theplatform hull 12 can be constructed of other known configurations. Forexample, multiple base structures that are configured to support thefloating wind turbine tower 1 in the ocean, a semisubmersible, or atension leg platform (TLP).

The floating wind turbine 1 experiences loads induced by wave activityand other environmental factors. In particular, ocean waves exert forcesagainst the platform top 11 which lead to undesirable performance of thefloating wind turbine 1 if not properly mitigated. A computing system,such as a pitch control mechanism, is operably coupled to the floatingwind turbine tower 1 for regulating and/or controlling blade pitchangles of the rotor blades. In a first exemplary embodiment, thecomputing system is one or more remote servers servicing components ofthe floating wind turbine 1, such as an onboard pitch controller. In asecond exemplary embodiment, the computing system is an onboard computerlocated internally to the floating wind turbine 1. The computing systemincludes components performed remotely and onboard the floating windturbine. By way of example, low-level controllers responsible for quickand fundamental decisions affecting the second-by-second performance ofthe motors/hydraulics/etc. can be implemented onboard the floating windturbine because communication delays/dropouts/faults in the networkwould require the turbine to shut down, while software is run on remoteservers located at the wind parks that execute some high levelprocessing and decision making (e.g., deciding whether to enable/disabledifferent functions based on weather conditions, etc.).

The computing system reduces floating wind turbine tower loads inducedby ocean waves by adjusting a blade pitch angle of at least one rotorblade 5 of a floating wind turbine 1 to minimize a moment imbalance atthe transition piece 7 between the platform top 11 and the tower bottom8 of the floating wind turbine 1 caused by ocean wave activity. Further,the computing system is part of a blade pitch control system describedin great detail infra.

FIG. 2 depicts a block diagram of blade pitch control system 100, inaccordance with embodiments of the present invention. The blade pitchcontrol system 100 is a system for regulating blade pitch angles ofrotor blades of a floating wind turbine tower to counteract a momentimbalance of the floating wind turbine caused by ocean wave activity.The blade pitch control system 100 may be alternatively referred to as apitch control mechanism, a load mitigation system, a floating windturbine tower system, a pitch regulator for floating wind turbines, aload reduction system, and the like. Moreover, the blade pitch controlsystem 100 includes a computing system 120. The computing system 120 canbe a computer system, a computer, a server, one or more servers, abackend computing system, and the like. The blade pitch control system100 depicted in FIG. 2 refers to embodiments where the computing system120 is remote from the floating wind turbine tower 1.

Furthermore, the blade pitch control system 100 includes the floatingwind turbine 1 and a bandpass filter 113 that are communicativelycoupled to the computing system 120 over a network 107. For instance,information/data is transmitted to and/or received from the floatingwind turbine tower 1 and the bandpass filter 113 over a network 107. Inan exemplary embodiment, the network 107 is a cloud computing network.Further embodiments of network 107 refer to a group of two or morecomputer systems linked together. Network 107 includes any type ofcomputer network known by individuals skilled in the art. Examples ofnetwork 107 include a LAN, WAN, campus area networks (CAN), home areanetworks (HAN), metropolitan area networks (MAN), an enterprise network,cloud computing network (either physical or virtual) e.g. the Internet,a cellular communication network such as GSM or CDMA network or a mobilecommunications data network. In one embodiment, the architecture of thenetwork 107 is a peer-to-peer, wherein in another embodiment, thenetwork 107 is organized as a client/server architecture.

In an exemplary embodiment, the network 107 further comprises, inaddition to the computing system 120, a connection to one or morenetwork-accessible knowledge bases 114, which are network repositoriescontaining information of floating wind turbines, blade pitch angledata, load data, environmental condition data, etc., networkrepositories or other systems connected to the network 107 that areconsidered nodes of the network 107. In an embodiment where thecomputing system 120 or network repositories allocate resources to beused by the other nodes of the network 107, the computing system 120 andnetwork-accessible knowledge bases 114 is referred to as servers.

The network-accessible knowledge bases 114 is a data collection area onthe network 107 which backs up and save all the data transmitted backand forth between the nodes of the network 107. For example, the networkrepository is a data center saving and cataloging the information offloating wind turbines, blade pitch angle data, load data, environmentalcondition data, etc., and the like, to generate both historical andpredictive reports regarding a blade pitch angle adjustment. In anexemplary embodiment, a data collection center housing thenetwork-accessible knowledge bases 114 includes an analytic modulecapable of analyzing each piece of data being stored by thenetwork-accessible knowledge bases 114. Further, the computing system120 can be integrated with or as a part of the data collection centerhousing the network-accessible knowledge bases 114. In an alternativeembodiment, the network-accessible knowledge bases 114 are a localrepository that is connected to the computing system 120.

The floating wind turbine 1 includes at least one rotor blade sensor110, at least one transition piece or platform top sensor 111, and apitch controller 112. The transition piece sensor 111 can be locatedeither in the tower bottom 8 or the platform top 11. The rotor bladesensor(s) 110 measures thrust force of the rotor blades and the platformtop/transition piece sensor 111 measures forces acting on the platformtop 11 and/or the transition piece 7 of the floating wind turbine 1.Examples of the sensors 110 and 111 include strain gauges, Fiber Bragggrating sensors (FBGS, accelerometers, piezoelectric sensors, and thelike. The pitch controller 112 is responsible for sending commands tothe rotor blades for adjusting the blade pitch angle of the rotorblades. In an exemplary embodiment, the pitch controller 112 is aproportional-integral-derivative (PID) controller. The pitch controller112 includes other modules that control pitch damage attenuation, speedregulation, etc.

FIG. 3 depicts a block diagram of an alternative blade pitch controlsystem 100′, in accordance with embodiments of the present invention.The blade pitch control system 100′ depicted in FIG. 3 refers toembodiments where the computing system 120 is an onboard computer of thefloating wind turbine tower 1.

The computing system 120 of the blade pitch control system 100, 100′ isequipped with a memory device 142 which stores variousdata/information/code, and a processor 141 for implementing the tasksassociated with the blade pitch control system 100, 100′. A blade pitchangle adjustment application 130 is loaded in the memory device 142 ofthe computing system 120. The blade pitch angle adjustment application130 can be an interface, an application, a program, a module, or acombination of modules. In an exemplary embodiment, the blade pitchangle adjustment application 130 is a software application running oncomputing system 120.

Referring back to FIG. 2, the blade pitch angle adjustment application130 of the computing system 120 includes an error signal module 131, afilter module 132, a conversion module 133, and an adjustment module134. A “module” refers to a hardware-based module, a software-basedmodule, or a module that is a combination of hardware and software.Hardware-based modules include self-contained components such aschipsets, specialized circuitry and one or more memory devices, while asoftware-based module is a part of a program code or linked to theprogram code containing specific programmed instructions, which isloaded in the memory device of the computing system 120. A module(whether hardware, software, or a combination thereof) is designed toimplement or execute one or more particular functions or routines.

The error signal module 131 includes one or more components of hardwareand/or software program code for calculating an error signal defined bya moment imbalance between a tower bottom moment and a thrust moment ofthe floating wind turbine. FIG. 4 depicts a schematic view of thefloating wind turbine 1 of FIG. 1, showing a thrust moment M_(T) and atower bottom moment M_(B), in accordance with embodiments of the presentinvention. The tower bottom moment M_(B) is a moment at the transitionpiece 7/platform top 11 of the floating wind turbine 1 as a result ofenvironmental loads. The value of the tower bottom moment M_(B) ismeasured by the platform top/transition piece sensor 111 or can beestimated from other data received from other sensors (e.g. straingauge). The thrust moment M_(T) is a moment defined at a location at atower section 4 of the floating wind turbine 1 proximate the platformtop 11 and transition piece 7, computed from a thrust force T_(F) ofrotor blades of the floating wind turbine measured by the rotor bladesensors 110. The thrust moment M_(T) is defined as the thrust forceT_(F) multiplied by a distance or height H_(Ref) of the tower measuredfrom the transition piece 7 (i.e. H_(Ref)×T_(F)).

The moment imbalance is thus the difference between the thrust momentM_(T) and the tower bottom moment M_(B). The error signal ε iscalculated by the error signal module 131 in response to the computingsystem 120 receiving or obtaining the values of the thrust force T_(F)and the tower bottom moment M_(B), in accordance with the followingequation: ε=M_(B)−(H_(Ref)×T_(F)). The error signal ε comprisesfrequencies attributable to various disturbances, including ocean waveactivity. For instance, the error signal comprises frequenciesattributable to one or more of: turbulence due to wind above sea level,ocean wave activity, ocean current variability, vortex inducedvibrations, structural resonances, electrical grid phenomena, normalturbine operations, and the like. The frequencies in the error signalthat are not attributable to ocean wave activity are unwanted for thepurposes of counteracting the moment imbalance specifically due to oceanwave activity. Therefore, the unwanted signals are filtered out of theerror signal.

The filter module 132 includes one or more components of hardware and/orsoftware program code for filtering the error signal in a frequencyrange attributable to ocean wave activity to eliminate frequenciescontributing to the error signal that are not attributable to ocean waveactivity. The frequencies that are not attributable to ocean waveactivity are filtered out to ensure that the computed error signal ε andresulting blade pitch offset (Δβ) calculated by the computing system 120respond specifically to ocean wave activity while remaining relativelyinsensitive to the various other disturbances, which are either deemednegligible or compensated for by other modules of the blade pitchcontrol system. The filtering by the filter module 132 results in afiltered error signal. The filter module 132 filters the error signalusing a bandpass filter tuned to filter out frequencies above or belowthe frequency range attributable to ocean wave activity. The frequencyrange used corresponds to the ocean wave spectrum. In an exemplaryembodiment, the ocean wave frequency spectrum is in a range ofapproximately 0.03 Hz to 0.25 hz. Thus, the filter module 132 isolateswave excitation frequencies from the error signal that are in thefrequency range defined by an ocean wave spectrum, as shownschematically in FIG. 5. FIG. 5 graphically depicts the error signalbeing filtered so that frequencies only within the range of the oceanwave spectrum pass while the frequencies outside the ocean wave spectrumare stopped. In the illustrated embodiment, the range of the ocean wavespectrum is defined between a left frequency f_(L) limit and a rightfrequency limit f_(R); a center frequency is shown as f_(C). B is thepassband, the frequency range passed by the filter which is set to bethe ocean wave spectrum, 0 dB is pure passing and −3 dB is the pointwhere the input signal is considered completely filtered out, and thusoutput by the filter module 132 as a filtered error signal. The filterederror signal is then converted to a pitch offset signal.

Referring back to FIG. 2, the conversion module 133 includes one or morecomponents of hardware and/or software program code for converting thefiltered error signal to a pitch offset signal. For instance, theconversion module 133 converts the filtered error signal into a pitchoffset signal (Δβ) representing a difference to be applied to the actualblade pitch angle, β. In other words, the conversion module 133 convertsthe filtered error signal to the pitch offset signal by calculating adifference between an actual pitch angle of at least one rotor blade anda desired blade pitch angle of at least one rotor blade, wherein thedifference defines the pitch offset signal. By way of example, if one ofthe blades currently has a blade pitch angle of 3°, and the filterederror signal suggests that the blade pitch angle of the blade should beadjusted to 3.25°, the offset pitch signal is then the blade pitch0.25°. Each rotor blade may have a different actual blade pitch angle sothe conversion of the filtered error signal to the pitch offset signalmay have a different value with respect to each blade.

The conversion from the error signal to the pitch offset is based onthree terms: a value of the error itself, scaled by some amount k_(p)(proportional), how much the error is building up over time,approximated using a time integral of the error signal, scaled by someamount k_(i) (integral), and how much the value of the error ischanging, approximated using a time derivative of the error signal,scaled by some amount k_(d) (derivative). The scales k_(p), k_(i), k_(d)are used to adjust how much each term contributes to the finaladjustment to the pitch offset Δβ:

${\Delta\beta} = {{k_{p} \cdot ɛ} + {k_{i}{\int{ɛdt}}} + {k_{d}\frac{dɛ}{dt}}}$

In an exemplary embodiment, the pitch offset signal is calculated fromthe filtered error signal according to a function with termsproportional to a current value of the filtered error signal, a timeintegral of the filtered error signal, and a time derivative of thefiltered error signal.

The adjustment module 134 includes one or more components of hardwareand/or software program code for adjusting a blade pitch angle of atleast one rotor blade of the floating wind turbine according to thepitch offset signal. For instance, the adjustment module 134 sendsinstructions to the pitch controller 112 of the floating wind turbine 1to adjust a blade pitch angle of one or more rotor blades. Continuingwith the above example, if the pitch offset signal is 0.25°, theadjustment module 134 sends instructions to the pitch controller 112 toadjust the blade pitch angle of one of the blades by 0.25°. Theadjustment module 134 adjusts the blade pitch angle of each rotor bladeindependently of the other blades. In an exemplary embodiment, theadjustment module 134 adjusts the blade pitch angle for all of the rotorblades according to a pitch offset signal unique to the particularblade. In another exemplary embodiment, the adjustment module 134adjusts the blade pitch angle for only one of the rotor blades or two ofthe three rotor blades according to a pitch offset signal unique to theblades selected for adjustment.

Various tasks and specific functions of the modules of the computingsystem 120 may be performed by additional modules, or may be combinedinto other module(s) to reduce the number of modules. Further, anembodiment of the computer or computer system 120 comprises specialized,non-generic hardware and circuitry (i.e., specialized discretenon-generic analog, digital, and logic-based circuitry) (independentlyor in combination) particularized for executing only methods of thepresent invention. The specialized discrete non-generic analog, digital,and logic-based circuitry includes proprietary specially designedcomponents (e.g., a specialized integrated circuit, such as for examplean Application Specific Integrated Circuit (ASIC), designed for onlyimplementing methods of the present invention).

Furthermore, the blade pitch control system 100, 100′ uses specifichardware, such as pitch controllers, wind turbine components, sensors,to calculate a pitch offset signal to counteract a moment induced byocean wave activity of a floating wind turbine. The rotor blades of thefloating wind turbine are physically moved to change a blade pitch angleof the blades to minimize the moment imbalance of the floating windturbine towers which is a practical application of a technical solutionthat improves the efficiency of the floating wind turbine and allows forthe floating wind turbine to be designed with less material cost, usingthe blade pitch control system 100, 100′ to counteract a momentimbalance as opposed to modifying the structural configuration of theplatform hull and the floating wind turbine tower.

Referring now to FIG. 6, which depicts a flow chart of a method 200 forreducing loads induced by ocean waves on a floating wind turbine, inaccordance with embodiments of the present invention. One embodiment ofa method 200 or algorithm that may be implemented for reducing loadsinduced by ocean waves on a floating wind turbine with the blade pitchcontrol system 100, 100′ described in FIGS. 1-5 using one or morecomputer systems as defined generically in FIG. 9 below, and morespecifically by the specific embodiments of FIGS. 2-3.

Embodiments of the method 200 for reducing loads induced by ocean waveson a floating wind turbine, in accordance with embodiments of thepresent invention, may begin with receiving the shaft thrust force T_(f)and the tower bottom moment M_(B) values. The shaft thrust force T_(f)and the tower moment M_(B) values may be measured by one or more sensorsof the floating wind turbine, in which the sensor data is transmitted tothe computing system 120. The shaft thrust force T_(f) is used incombination with the length or height H_(ref) of the tower measuredbetween the rotor blades and the transition section 7 where the towersection meets the platform top 111 to calculate the thrust moment M_(T).Step 201 calculates an error between the tower bottom moment M_(B) andthe thrust moment M_(T). The output of step 201 is the error signal 21representing the moment imbalance occurring at the transition piece 7 ofthe floating wind turbine tower 1. Step 202 filters the error signal 21in a frequency range where ocean energy is concentrated to eliminateunwanted frequencies associated with disturbances not attributable toocean wave activity. In an exemplary embodiment, a custom bandpassfilter is used that is configured to isolate wave excitation frequenciesfrom the error signal 21 that are in the frequency range defined by anocean wave spectrum. The output of step 202 is the filtered error signal22. The filtered error signal 22 is a signal having a frequency thatrepresents a moment, although other units can be used depending on thecustom bandpass filter used. Step 203 converts the filtered error signal22.

FIG. 7 depicts a flowchart of the converting step 203 of the method 200for reducing loads induced by ocean waves on a floating wind turbine, inaccordance with embodiments of the present invention. Step 301determines an actual blade pitch angle of at least one rotor blade.Using the filtered error signal 22, step 302 determines a desired bladepitch angle of the at least one rotor blade. Step 303 calculates adifference between the actual blade pitch angle of the at least onerotor blade and the desired blade pitch angle of the at least one rotorblade to obtain a pitch offset signal 23 for adjusting the blade pitchangle of the at least one rotor blade. The converting step 203 can bedone for one, some, or all of the rotor blades. The output of theconverting step 203 is a pitch offset signal 23 and potentially pitchoffset signals for additional rotor blades 23′, 23″. Referring back toFIG. 6, step 204 adjusts the blade pitch angle of one or more rotorblades according to the pitch offset signals 23, 23′, 23″.

FIG. 8 depicts a schematic block diagram of the blade pitch angleadjustment of the method 200 for reducing loads induced by ocean waveson a floating wind turbine, in accordance with embodiments of thepresent invention. The pitch offset signals 23, 23′, 23″ are transmittedto a pitch controller of the floating wind turbine that controls thepitch of the rotor blades. The pitch controller adjusts the blade pitchangle of “Blade 1” according to pitch offset signal 23. The pitchcontroller adjusts the blade pitch angle of “Blade 2” according to pitchoffset signal 23′. The pitch controller adjusts the blade pitch angle of“Blade 3” according to pitch offset signal 23″. By way of example, ifthe pitch offset signal 23 is 0.24°, then “Blade 1” is adjusted 0.24°from a current blade pitch angle position. Likewise, if the pitch offsetsignal 23′ is 0.37° and the pitch offset signal 23″ is 0.15°, then“Blade 2” is adjusted 0.37° from a current blade pitch angle positionand “Blade 3” is adjusted 0.15° from a current blade pitch angleposition.

Accordingly, method 200 counteracts the moment imbalance of the floatingwind turbine tower by regulating the pitch control of the blades so thatthe tower bottom moment and the thrust moment cancel each other out,thereby reducing and/or eliminating a transfer of loads from theplatform hull 12 to the platform top 11 induced specifically by oceanwaves.

FIG. 9 depicts a block diagram of a computer system for the blade pitchcontrol system 100, 100′ of FIGS. 1-5, capable of implementing methodsfor reducing loads induced by ocean waves on a floating wind turbine ofFIGS. 6-8, in accordance with embodiments of the present invention. Thecomputer system 500 may generally comprise a processor 591, an inputdevice 592 coupled to the processor 591, an output device 593 coupled tothe processor 591, and memory devices 594 and 595 each coupled to theprocessor 591. The input device 592, output device 593 and memorydevices 594, 595 may each be coupled to the processor 591 via a bus.Processor 591 may perform computations and control the functions ofcomputer system 500, including executing instructions included in thecomputer code 597 for the tools and programs capable of implementing amethod for reducing loads induced by ocean waves on a floating windturbine in the manner prescribed by the embodiments of FIGS. 6-8 usingthe blade pitch control system 100, 100′ of FIGS. 1-5, wherein theinstructions of the computer code 597 may be executed by processor 591via memory device 595. The computer code 597 may include software orprogram instructions that may implement one or more algorithms forimplementing the method for reducing loads induced by ocean waves on afloating wind turbine, as described in detail above. The processor 591executes the computer code 597. Processor 591 may include a singleprocessing unit, or may be distributed across one or more processingunits in one or more locations (e.g., on a client and server).

The memory device 594 may include input data 596. The input data 596includes any inputs required by the computer code 597. The output device593 displays output from the computer code 597. Either or both memorydevices 594 and 595 may be used as a computer usable storage medium (orprogram storage device) having a computer-readable program embodiedtherein and/or having other data stored therein, wherein thecomputer-readable program comprises the computer code 597. Generally, acomputer program product (or, alternatively, an article of manufacture)of the computer system 500 may comprise said computer usable storagemedium (or said program storage device).

Memory devices 594, 595 include any known computer-readable storagemedium, including those described in detail below. In one embodiment,cache memory elements of memory devices 594, 595 may provide temporarystorage of at least some program code (e.g., computer code 597) in orderto reduce the number of times code must be retrieved from bulk storagewhile instructions of the computer code 597 are executed. Moreover,similar to processor 591, memory devices 594, 595 may reside at a singlephysical location, including one or more types of data storage, or bedistributed across a plurality of physical systems in various forms.Further, memory devices 594, 595 can include data distributed across,for example, a local area network (LAN) or a wide area network (WAN).Further, memory devices 594, 595 may include an operating system (notshown) and may include other systems not shown in FIG. 9.

In some embodiments, the computer system 500 may further be coupled toan Input/output (I/O) interface and a computer data storage unit. An I/Ointerface may include any system for exchanging information to or froman input device 592 or output device 593. The input device 592 may be,inter alia, a keyboard, a mouse, etc. or in some embodiments thetouchscreen of a computing device. The output device 593 may be, interalia, a printer, a plotter, a display device (such as a computerscreen), a magnetic tape, a removable hard disk, a floppy disk, etc. Thememory devices 594 and 595 may be, inter alia, a hard disk, a floppydisk, a magnetic tape, an optical storage such as a compact disc (CD) ora digital video disc (DVD), a dynamic random access memory (DRAM), aread-only memory (ROM), etc. The bus may provide a communication linkbetween each of the components in computer 500, and may include any typeof transmission link, including electrical, optical, wireless, etc.

An I/O interface may allow computer system 500 to store information(e.g., data or program instructions such as program code 597) on andretrieve the information from computer data storage unit (not shown).Computer data storage unit includes a known computer-readable storagemedium, which is described below. In one embodiment, computer datastorage unit may be a non-volatile data storage device, such as amagnetic disk drive (i.e., hard disk drive) or an optical disc drive(e.g., a CD-ROM drive which receives a CD-ROM disk). In otherembodiments, the data storage unit may include a knowledge base or datarepository 125 as shown in FIG. 2.

As will be appreciated by one skilled in the art, in a first embodiment,the present invention may be a method; in a second embodiment, thepresent invention may be a system; and in a third embodiment, thepresent invention may be a computer program product. Any of thecomponents of the embodiments of the present invention can be deployed,managed, serviced, etc. by a service provider that offers to deploy orintegrate computing infrastructure with respect to assisted learningwith a portable computing device. Thus, an embodiment of the presentinvention discloses a process for supporting computer infrastructure,where the process includes providing at least one support service for atleast one of integrating, hosting, maintaining and deployingcomputer-readable code (e.g., program code 597) in a computer system(e.g., computer system 500) including one or more processor(s) 591,wherein the processor(s) carry out instructions contained in thecomputer code 597 causing the computer system to reduce loads induced byocean waves on a floating wind turbine. Another embodiment discloses aprocess for supporting computer infrastructure, where the processincludes integrating computer-readable program code into a computersystem 500 including a processor.

The step of integrating includes storing the program code in acomputer-readable storage device of the computer system 500 through useof the processor. The program code, upon being executed by theprocessor, implements a method for reducing loads induced by ocean waveson a floating wind turbine. Thus, the present invention discloses aprocess for supporting, deploying and/or integrating computerinfrastructure, integrating, hosting, maintaining, and deployingcomputer-readable code into the computer system 500, wherein the code incombination with the computer system 500 is capable of performing amethod for reducing loads induced by ocean waves on a floating windturbine.

A computer program product of the present invention comprises one ormore computer-readable hardware storage devices having computer-readableprogram code stored therein, said program code containing instructionsexecutable by one or more processors of a computer system to implementthe methods of the present invention.

A computer system of the present invention comprises one or moreprocessors, one or more memories, and one or more computer-readablehardware storage devices, said one or more hardware storage devicescontaining program code executable by the one or more processors via theone or more memories to implement the methods of the present invention.

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer-readable storagemedium (or media) having computer-readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer-readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer-readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer-readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer-readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer-readable program instructions described herein can bedownloaded to respective computing/processing devices from acomputer-readable storage medium or to an external computer or externalstorage device via a network, for example, the Internet, a local areanetwork, a wide area network and/or a wireless network. The network maycomprise copper transmission cables, optical transmission fibers,wireless transmission, routers, firewalls, switches, gateway computersand/or edge servers. A network adapter card or network interface in eachcomputing/processing device receives computer-readable programinstructions from the network and forwards the computer-readable programinstructions for storage in a computer-readable storage medium withinthe respective computing/processing device.

Computer-readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine-dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer-readable program instructions may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer-readable program instructions by utilizing state information ofthe computer-readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer-readable program instructions.

These computer-readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer-readable program instructionsmay also be stored in a computer-readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that thecomputer-readable storage medium having instructions stored thereincomprises an article of manufacture including instructions whichimplement aspects of the function/act specified in the flowchart and/orblock diagram block or blocks.

The computer-readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce acomputer-implemented process, such that the instructions which executeon the computer, other programmable apparatus, or other device implementthe functions/acts specified in the flowchart and/or block diagram blockor blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

While this disclosure has been described in conjunction with thespecific embodiments outlined above, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, the preferred embodiments of thepresent disclosure as set forth above are intended to be illustrative,not limiting. Various changes may be made without departing from thespirit and scope of the invention, as required by the following claims.The claims provide the scope of the coverage of the invention and shouldnot be limited to the specific examples provided herein.

1. A method for reducing floating wind turbine loads induced by oceanwaves, the method comprising: adjusting a blade pitch angle of at leastone rotor blade of a floating wind turbine to minimize a momentimbalance at a platform top of a floating wind turbine caused by oceanwave activity.
 2. The method of claim 1, further comprising calculatingan error signal based on the moment imbalance measured between a towerbottom moment and a thrust moment.
 3. The method of claim 2, wherein thetower bottom moment is a moment at a platform top of the floating windturbine as a result of environmental loads, and the thrust moment is amoment defined by a thrust force of rotor blades of the floating windturbine measured at a location on the shaft of the floating turbineproximate the platform top.
 4. The method of claim 2, furthercomprising: filtering the error signal using a bandpass filter in afrequency range attributable to ocean wave activity to obtain a filterederror signal.
 5. The method of claim 4, wherein the filtering isolateswave excitation frequencies from the error signal that are in thefrequency range defined by an ocean wave spectrum.
 6. The method ofclaim 4, wherein the blade pitch angle is adjusted according to a pitchoffset signal converted from the filtered error signal.
 7. The method ofclaim 6, wherein the pitch offset signal is converted from the filterederror signal by calculating a difference between an actual pitch anglevalue of at least one rotor blade and a desired blade pitch angle of atleast one rotor blade, wherein the difference defines the pitch offsetsignal.
 8. A method for reducing loads induced by ocean waves on afloating wind turbine, the method comprising: calculating, by aprocessor of a computing system, an error signal defined by a momentimbalance between a tower bottom moment and a thrust moment of thefloating wind turbine; filtering, by the processor, the error signal ina frequency range attributable to ocean wave activity to eliminatefrequencies contributing to the error signal that are not attributableto ocean wave activity, resulting in a filtered error signal;converting, by the processor, the filtered error signal to a pitchoffset signal; and adjusting, by the processor, a blade pitch angle ofat least one rotor blade of the floating wind turbine according to thepitch offset signal.
 9. The method of claim 8, wherein the tower bottommoment is a moment at a platform top of the floating wind turbine as aresult of environmental loads, and the thrust moment is a moment definedby a thrust force of rotor blades of the floating wind turbine measuredat a location at a tower section of the floating turbine proximate theplatform top.
 10. The method of claim 8, wherein the error signalcomprises frequencies attributable to one or more of: turbulence due towind above sea level, ocean wave activity, ocean current variability,vortex induced vibrations, structural resonances, electrical gridphenomena, and normal turbine operations.
 11. The method of claim 11,wherein the error signal is filtered using a bandpass filter tuned tofilter out frequencies above or below the frequency range attributableto ocean wave activity.
 12. The method of claim 11, wherein thefrequency range attributable to ocean wave activity is defined by anocean wave frequency spectrum in a range of approximately 0.03 Hz to0.25 Hz.
 13. The method of claim 8, wherein the converting the filterederror signal to the pitch offset signal includes calculating adifference between an actual pitch angle value of at least one rotorblade and a desired blade pitch angle of at least one rotor blade,wherein the difference defines the pitch offset signal.
 14. The methodof claim 8, wherein the pitch offset signal is calculated from thefiltered error signal according to a function with the followingproperties: a term proportional to a current value of the filtered errorsignal; a term proportional to a time integral of the filtered errorsignal; and a term proportional to a time derivative of the filterederror signal
 15. A computer system, comprising: a processor; a memorydevice coupled to the processor; a pitch controller coupled to theprocessor; and a computer readable storage device coupled to theprocessor, wherein the storage device contains program code executableby the processor via the memory device to implement a method forreducing loads induced by ocean waves on a floating wind turbine tower,the method comprising: calculating, by a processor of a computingsystem, an error signal defined by a moment imbalance between a towerbottom moment and a thrust moment of the floating wind turbine;filtering, by the processor, the error signal in a frequency rangeattributable to ocean wave activity to eliminate frequenciescontributing to the error signal that are not attributable to ocean waveactivity, resulting in a filtered error signal; converting, by theprocessor, the filtered error signal to a pitch offset signal; andadjusting, by the processor, a blade pitch angle of at least one rotorblade of the floating wind turbine according to the pitch offset signal.16. The computer system of claim 15, wherein the tower bottom moment isa moment at a platform top of the floating wind turbine as a result ofenvironmental loads, and the thrust moment is a moment defined by athrust force of rotor blades of the floating wind turbine measured at alocation of a tower section of the floating turbine proximate theplatform top.
 17. The computer system of claim 15, wherein the errorsignal is filtered using a bandpass filter tuned to filter outfrequencies above or below the frequency range attributable to oceanwave activity, further wherein the frequency range attributable to oceanwave activity is defined by an ocean wave frequency spectrum in a rangeof approximately 0.03 Hz to 0.25 Hz.
 18. The computer system of claim15, wherein the converting the filtered error signal to the pitch offsetsignal includes calculating a difference between an actual pitch anglevalue of at least one rotor blade and a desired blade pitch angle of atleast one rotor blade, wherein the difference defines the pitch offsetsignal.
 19. A computer program product, comprising a computer readablehardware storage device storing a computer readable program code, thecomputer readable program code comprising an algorithm that whenexecuted by a computer processor of a computing system implements amethod according to claim 8.